Flex The FLEX machine was invented by Alan Kay and Ed Cheadle, as a personal computing project--an attempt to make the most possible from limited space and limited resources. In the FLEX machine, Kay and Cheadle created an entirely object-oriented PC. The development of FLEX took a cue from Douglas Engelbart's ideas, and it can be characterized as the first machine with the goal of being extremely "user-friendly." The FLEX machine had an interactive interface, built with an OOPL that made interfacing between man and machine facile, and was intended to "augment" the human intellect through interaction with the machine. The interface chosen for the FLEX machine was one very similar to the SketchPad interface; Kay writes that "Sketchpad's notion of a general window that viewed a larger virtual world was a better idea than restricted horizontal panes." [Kay93] The control structure of the FLEX machine was influenced heavily by SIMULA; Kay writes that "As in Simula, a coroutine control structure was used as a way to suspend and resume objects." [Kay93] The FLEX machine served as the precursor for Kay's other work on object-oriented machines, such as . These ideas culminated in the development of the Smalltalk environment.